Alkylation aide for sulfuric acid catalyzed alkylation units

ABSTRACT

Hydrocarbon alkylation processes which are catalyzed by acids are promoted by the addition of an alkylation promoter which is a combination of a new carboxylic acid having the structural formula &lt;IMAGE&gt;   wherein R, R1 and R2 are alkyl groups and at least one aromatic hydrocarbon sulfonic acid selected from compounds having the structure   &lt;IMAGE&gt;  wherein R3 is H or an alkyl group and R4 is an alkyl group.

FIELD OF THE INVENTION

This invention relates to a process for alkylating hydrocarbons and moreparticularly to an improved process of alkylating aliphatichydrocarbons, particularly branched-chain aliphatic hydrocarbons witholefinic hydrocarbons in the presence of a strong acid.

BACKGROUND

The value of hydrocarbons can often be enhanced by alkylation of lowerhydrocarbons to produce higher molecular weight hydrocarbons. Forexample, isobutanes can be alkylated with isobutene to produceisooctane, which is valuable for increasing the octane rating ofgasoline. A common commercial method for alkylating a hydrocarbon is toreact the hydrocarbon with selected olefins in the presence of a strongacid, such as sulfuric acid. Unfortunately, such acid, solutions are notreadily miscible with organic liquids. Consequently, in alkylationprocesses catalyzed by strong acids, it has been necessary to use aconsiderable excess of acid to effect a commercially feasible degree ofalkylation. The unused acid is discarded with the spent acid, therebyreducing the efficiency of the process and augmenting the alreadyburdensome waste disposal problem. Improvements which will reduce theamount of acid waste have long been sought.

PRIOR ART

In attempts to improve the efficiency of acid catalyzed alkylationsreaction temperatures have been lowered, the mixing efficiency has beenincreased and the ratio of hydrocarbon to olefin has been varied. Noneof these techniques has meet with significant success.

Chemical approaches have also been attempted. For example, variouschemicals have been added to acid-catalyzed alkylation reaction mixturesto promote more efficient use of the acid catalyst. Thus, U.S. Pat. No.3,324,196, issued to Kramer et al, discloses the use of an amine oramide containing at least one C₈ to C₂₀ aliphatic group to promote theacid-catalyzed alkylation of aliphatic and aromatic hydrocarbons. U.S.Pat. No. 2,880,255 discloses the use of mercaptans or combinations ofaliphatic amines and mercaptans to promote the alkylation ofhydrocarbons.

Carboxylic acids have also been used to promote acid-catalyzedalkylation reactions. For example, U.S. Pat. No. 3,778,489 discloses theuse of carboxylic acids having 1 to 10 carbon atoms as promoters for thesulfuric acid-catalyzed alkylation of a paraffin with a combination ofolefins. U.S. Pat. No. 3,766,293 discloses the use of carboxylic acidshaving 2 to 10 carbon atoms as promoters for the flurosulfuricacid-catalyzed alkylation of a paraffin with an olefin. U.S. Pat. No.2,286,184 discloses the use of low molecular weight mono-carboxylic anddicarboxylic acids as modifiers for the sulfuric acid catalyzedalkylation of isoparaffins and olefins.

The present invention is based on the use of certain organic to promotealkylation reactions. It has been discovered that these organic acidsincrease the efficiency of acid-catalyzed alkylation reactions.Accordingly, it is an object of the invention to present an improvedalkylation process. It is another object of the invention to present animproved process for alkylating hydrocarbons with acid catalyst. It isanother object of the invention to reduce the acid consumption inacid-catalyzed alkylation reactions. These and other objects of theinvention are supported in the following description and examples of theinvention.

SUMMARY OF THE INVENTION

It has now been discovered that the highly efficient alkylation ofaliphatic hydrocarbons by means of strong acid catalysts can be effectedby carrying out the alkylation reaction in the presence of a mixture ofat least one neo carboxylic acid having the structure ##STR3## whereinR, R¹ and, R² are alkyl groups and the average total sum of the carbonatoms in R, R¹ and, R² usually varies from 3 to about 30 or more and atleast one aromatic hydrocarbon sulfonic acid. In preferred neocarboxylic acids R, R¹ and R² contain an average total of 3 to about 10carbon atoms. Preferred aromatic hydrocarbon sulfonic acids are thealkyl-substituted benzene sulfonic acids. Particularly preferredaromatic sulfonic acids contain 1 to about 16 total alkyl carbon atoms.

DETAILED DESCRIPTION

Suitable Neo acids useable in the invention are commercially availablefrom Exxon Chemical Company under the name Neo Acids or from ShellChemical Company under the name Versatic Acids® or they may be preparedby methods such as described in the article "Neoacids" by Feffer,Journal of the American Oil Chemists Society, 55 342A (1978). The methodof preparation of the neo acids is well known and forms no part of thisinvention.

The neo acid may be a pure acid or a mixture of isomers of a neo acid orit may be a mixture of various molecular weight neo acids. The averagetotal number of carbon atoms in the alkyl radicals attached to the alphacarbon atom of these acids may range as high as 30 or more. The averageof the total number of carbon atoms in the alpha alkyl radicals isdesirably in the range of 3 to about 30 carbon atoms. When the neo acidis trimethyl acetic acid the sum of R, R¹ and R² will, of course, be 3.Preferred neo acids are those in which the average total number ofcarbon atoms in R, R¹ and R³ is 3 to 10.

Typical neo acids that fall within the above description includeneopentanoic acid, mixed neodecanoic acids, 2,2-dimethyl heptadecanoicacid, triethyl acetic acid, dimethyl pentyl acetic acid, etc. Preferredneo acids are trimethyl acetic acid and the pure or mixed neodecanoicacids.

Aromatic sulfonic acids usable in this invention include the aromatichydrocarbon sulfonic acids having 7 to about 46 or more carbon atoms.Although sulfonic acids having more than 46 carbon atoms can be used inthe invention sulfonic acids having no more than about 46 carbon atomsare preferred because they are more readily available and are easier tohandle. In the preferred embodiment the aromatic hydrocarbon sulfonicacid has 1 to about 16 aliphatic carbon atoms. The most common aromaticsulfonic acids include the saturated and ethylenically unsaturatedaliphatic hydrocarbon-substituted benzene sulfonic acids having 1 toabout 40 aliphatic carbon atoms. As can be appreciated mixtures of twoor more aromatic hydrocarbon sulfonic acids can be used in theinvention. Suitable aliphatic hydrocarbon-substituted benzene sulfonicacids include those having the formula ##STR4## wherein R³ is hydrogenor a straight or branched chain saturated or ethylenically unsaturatedaliphatic hydrocarbon group and R⁴ is a straight or branched chainsaturated or ethylenically unsaturated aliphatic hydrocarbon group. Thetotal number of carbon atoms in R³ and R⁴ generally varies from 1 toabout 40 and preferably varies from 1 to about 16. When R³ and R⁴ areboth aliphatic hydrocarbon groups they can be identical or different.The aliphatic hydrocarbon groups may be in any ring position relative tothe sulfonic acid radical but in the preferred embodiment one group isin the para position. Typical aromatic sulfonic acids include p-toluenesulfonic acid, p-t-butyl benzene sulfonic acid, mixed dodecyl benzenesulfonic acids, o-hexadecylbenzene sulfonic acid, p-eicosyl benzenesulfonic acid, mixed xylene sulfonic acids, o-methyl-m-di-dodecylbenzene sulfonic acid, etc. The preferred aromatic hydrocarbon sulfonicacids are the alkyl-substituted benzene sulfonic acids, such asp-toluene sulfonic acid, p-t-butyl sulfonic acid, p-dodecyl benzenesulfonic acid, etc.

The preparation of the aromatic hydrocarbon sulfonic acids is well knownand forms no part of this invention. Several aromatic hydrocarbonsulfonic acids are available commercially.

The carboxylic/sulfonic acid mixture may be used in any acid-catalyzedalkylation reaction between hydrocarbons and olefins. Hydrocarbons whichare often alkylated include saturated aliphatic and cycloaliphatichydrocarbons and aromatic hydrocarbons. The alklylation promoters of theinvention are particularly useful in the alkylation of lowerbranched-chain alkanes, such as isobutane and isopentane, with lowerolefins to produce octane rating improving additives for gasoline. Loweralkanes which are desirably alkylated include those having 4 to 10atoms.

Olefins which are used in alkylation reactions include those monoolefinshaving 3 to 10 carbon atoms. The olefins may be straight- orbranched-chain and the olefinic unsaturation may be located anywhere inthe structure of the molecule.

Particularly useful gasoline additives for increasing the octane ratingare the branched octanes, such as the compounds or mixture of compoundsobtained when isobutane is alkylated with mixed butenes. Branchedoctanes can also be prepared by the reaction of other alkanes andolefins, for example by the reaction of isopentane and propylene.

Various strong acids are useful for catalyzing the alkylation ofaliphatic or aromatic hydrocarbons with an olefin. Sulfuric acid,because of its efficiency and low cost, is the most commonly used acidalkylation catalyst. Other strong acids which can be used includehydrofluoric acid, phosphoric acid and fluorosulfonic acid. Any of theother well known strong acids are also useful for catalyzing alkylationreactions. Strong Lewis acids, such as aluminum bromide, aluminumchloride, antimony pentafluoride, antimony pentachloride, borontrifluoride, etc., can also be used as the acid catalyst in the processof this invention. In general, the alkylation promoters of the inventioncan be used with any known acid alkylation catalyst.

The alkylation reaction is carried out with all of the reactants in theliquid phase. The temperature of the reaction is that generally used foralkylation reactions. Reaction temperatures can vary from below 0° to ashigh as or higher than 200° F. The pressure of the reaction is notcritical and any pressure which will maintain the reactantssubstantially in the liquid phase may be employed. Pressures generallyrange from atmospheric to as high as 100 psi or higher.

The neo acid and sulfonic acid components are generally used in relativeconcentrations of about 95 to 40% neo acid and 5 to 60% sulfonic acid,and preferably about 80 to 50% neo acid and 20 to 50% sulfonic acid,based on the total weight of neo acid and sulfonic acid used in theinvention.

The total amount of alkylation promoter added to the reaction mixtureusually varies from about 0.0005 to 5.0 weight percent, based on thetotal weight of catalyzing acid present in the reaction mixture. Amountsless than 0.0005 weight percent generally produce insignificant resultsand amounts greater than about 5.0 weight percent are generallyunnecessary, although such higher concentrations can be used, ifdesired. The preferred promoter lower concentration is about 0.001percent and the most preferred minimum level is about 0.0025 percent,based on the total weight of acid catalyst in the reaction mixture. Thepreferred upper limit of the alkylation promoter concentration is about1.0 percent and the most preferred upper limit is about 0.5 percent,based on the total weight of acid catalyst in the reaction mixture. Theoptimum total amount of alkylation promoter will, of course, varydepending upon the particular promoters employed, the particular strongacid catalyst used and the particular hydrocarbons and olefins beingreacted.

The alkylation promoters of the invention may be used with otheradditives, if desired. For example, other alkylation promoters may beused in combination with the promoters of the invention or surfactantsor other agents may be added to the reaction mixture.

In a typical application of the invention the hydrocarbon to bealkylated, such as a lower branched-chain alkane, and an olefin areintroduced into a suitable alkylation reaction vessel at a controlledtemperature, usually in the range of about 40° to 60° F., and at apressure sufficiently high to maintain the reactants in the liquidstate. The ratio of alkylatable hydrocarbon to olefin alkylating agentis preferably maintained at a high ratio, e.g. about 10:1, to minimizethe amount of alkyl sulfate formed by the reaction of olefin withsulfuric acid. An acid alkylation catalyst, such as sulfuric acid, andthe alkylation promoters are introduced into the reactor, preferably ona continuous basis. At the end of the desired reaction period thefinished product is removed from the reaction vessel and separated fromthe spent acid. The reaction may be carried out on either a batch orcontinuous basis.

The invention is further illustrated in the following examples. Unlessindicated otherwise, parts and percentages are on a weight basis. Themixed neodecanoic acid used in the example is sold by Exxon ChemicalCompany and has an acid number of about 320 and a melting point of lessthan -40° C. This product has a structure of ##STR5## and a typicalsource distribution of (i) R=CH₃, R'=CH₃, R"=C₆ H₁₃ : . . . 31%

(ii) R<C₆ H₁₃, R'=CH₃, R">CH₃ : . . . 67%

(iii) R<C₆ H₁₃, R'>CH₃, R">CH₃ : . . . 2%

EXAMPLE

The efficiency of an alkylation reaction is dependent upon the contacttime between the alkylation catalyst and the hydrocarbon beingalkylated; the longer the contact time, the more efficient thealkylation reaction The alkylation aide increases thecatalyst-hydrocarbon contact time. This demonstrates the effectivenessof the alkylation aides of the invention. The test procedure is asfollows: Fifty ml of 98% H₂ SO₄ ml of iso-octane are introduced into a100 ml graduate cylinder having a ground glass stopper. In the controlrun no alkylation additive is used and in the comparative runs and therun illustrating the invention 500 ppm of alkylation aide are added tothe test mixture. The stoppered cylinder is mechanically shaken for 60seconds after additive introduction and the time required for theentrained H₂ SO₄ to separate from the hydrocarbon layer and the timerequired for the entrained hydrocarbon to separate from the H₂ SO₄ layerare measured. The results are tabulated in the table.

                  TABLE                                                           ______________________________________                                                       Conc. Separation Time (sec.)                                   Run  Additive        (ppm)   Hydrocarbon                                                                            H.sub.2 SO.sub.4                        ______________________________________                                        1    None (Control)  --      2.38     3.24                                    2    Mixed Neodecanoic                                                                             500     13.86    44.50                                        acid (98%) (Com-                                                              parative)                                                                3    Para toluene sulfonic                                                                         500     21.63    33.61                                        acid (Comparative)                                                       4    Acid mixture (50%                                                                             500     26.69    52.74                                        mixed neodecanoic                                                             acid, 50% para toluene                                                        sulfonic acid)                                                           ______________________________________                                    

As illustrated in the example, use of the alkylation aide of theinvention (Run 4) results in a significantly greater contact time inboth the hydrocarbon and H₂ SO₄ phases than does the use of the sameamount of the neodecanoic acid or the para toluene sulfonic acid alone(Runs 2 and 3).

Although the invention is described with particular reference tospecific examples it is understood that the invention includesvariations. For example, other hydrocarbons, such as aromatic compounds,may be alkylated or other olefins or acids may be used. The scope of theinvention is limited only by the breadth of the appended claims.

What is claimed is:
 1. In an alkylation process comprising contacting analkylatable hydrocarbon with an olefinic alkylating agent at alkylationconditions in the presence of an acid catalyst and an alkylationpromoter, the improvement comprising using in combination as thepromoter(a) at least one carboxylic acid having the structure ##STR6##wherein R, R¹ and R² are the same or different straight or branchedchains alkyl groups and the average total sum of carbon atoms in R, R¹and R² is 3 to 30, and (b) at least one aromatic hydrocarbon sulfonicacid having 7 to 46 carbon atoms.
 2. The improved process of claim 1wherein the average total sum of carbon atoms in R, R¹ and R² is 3 to10.
 3. The improved process of either of claims 1 or 2 wherein saidaromatic hydrocarbon sulfonic acid has 1 to 16 aliphatic carbon atoms.4. The improved process of either of claims 1 or 2 wherein said aromatichydrocarbon sulfonic acid is selected from compounds having thestructure ##STR7## wherein R³ is H or a straight- or branched-chainalkyl group and R⁴ is a straight- or branched-chain alkyl group and thetotal number of carbon atoms in R³ and R⁴ is 1 `to
 40. 5. In analkylation process comprising contacting an alkylatable hydrocarbon withan olefinic alkylating agent at alkylation conditions in the presence ofan acid catalyst and an alkylation promoter, the improvement comprisingusing in combination as the promoter(a) at least one carboxylic acidhaving the structure ##STR8## wherein R, R₁ and R² are the same ordifferent straight- or branched-chain alkyl groups and the average totalsum of carbon atoms in R, R¹ and R² is 3 to 30 and (b) at least aromatichydrocarbon sulfonic acid selected from compounds having the structure##STR9## wherein R³ is H or an alkyl group and R₄ is an alkyl group andthe total number of carbon atoms in R³ and R⁴ is 1 to
 40. 6. Theimproved process of claim 5 wherein the average total number of carbonatoms in R, R¹ and R² is 3 to
 10. 7. The improved process of either ofclaims 5 or 6 wherein the total number of carbon atoms in R³ and R⁴ is 1to
 16. 8. The improved process of claim 7 wherein R³ is H.